Fix volatile bool serialized as 1 or 0

Fixes #2029

CHANGELOG.md

@@ -5,6 +5,7 @@ HEAD
 ----
 
 * Fix warning `function returns incomplete class type` on IAR (issue #2001)
+* Fix `volatile bool` serialized as `1` or `0` instead of `true` or `false` (issue #2029)
 
 v6.21.4 (2023-12-07)
 -------

extras/tests/JsonVariant/types.cpp

@@ -140,6 +140,13 @@ TEST_CASE("volatile") {
   DynamicJsonDocument doc(4096);
   JsonVariant variant = doc.to<JsonVariant>();
 
+  SECTION("volatile bool") {  // issue #2029
+    volatile bool f = true;
+    variant.set(f);
+    CHECK(variant.is<bool>() == true);
+    CHECK(variant.as<bool>() == true);
+  }
+
   SECTION("volatile int") {
     volatile int f = 42;
     variant.set(f);

src/ArduinoJson/Variant/VariantImpl.hpp

@@ -137,7 +137,8 @@ VariantRefBase<TDerived>::is() const {
 template <typename TDerived>
 template <typename T>
 inline bool VariantRefBase<TDerived>::set(const T& value) const {
-  Converter<T>::toJson(value, getOrCreateVariant());
+  Converter<typename detail::remove_cv<T>::type>::toJson(value,
+                                                         getOrCreateVariant());
   MemoryPool* pool = getPool();
   return pool && !pool->overflowed();
 }